Hi @BoogieFever
Thank you for the information.
Your GPU (12 GB of VRAM) and system memory are more than adequate for this setup, so we can exclude them as bottlenecks.
“it either says there’s only one connected, or it throws a corrupted frame error”
This is a typical symptom of USB 3.0 bandwidth saturation. A ZED 2i in HD1080@30 mode generates about 250 MB/s of image data, while a single USB 3.0 host controller provides roughly 620 MB/s of usable bandwidth. When the limit is exceeded, the SDK reports corrupted frames, or cameras fail to open entirely. You can find more details here: Setting Up Multiple 3D Cameras | StereoLabs
Check your USB topology
Most add-on USB cards expose multiple ports, but they share a single internal host controller, so all the cameras connected to the card compete for the same bandwidth. Please verify how many independent host controllers your system actually has; on Windows you can use Device Manager (View > Devices by connection) or the USB Device Tree Viewer tool. The goal is a maximum of two cameras per controller, ideally one. If needed, replace the card with a PCIe expansion card providing one dedicated controller per port; this guide can also help: https://support.stereolabs.com/hc/en-us/articles/207635225-How-to-fix-USB-3-0-bandwidth-and-connection-issues
Also make sure you are using the original USB 3.0 cables, plugged into rear motherboard ports, without hubs or extensions.
Reduce the per-camera load
For body tracking fusion you do not need full resolution; setting all the cameras to HD720@30 significantly reduces the USB bandwidth and the processing load, and it is usually enough for reliable skeleton detection.
About performance
The RTX 3080 Ti is a good GPU for this task, but the i7-8700 is a 6-core CPU from 2017, and running four simultaneous grab and AI pipelines is very CPU intensive; this is most likely the reason for the low FPS you are experiencing even when the USB connection is stable. The “ghost skeletons” are instead a sign of imprecise extrinsic calibration; once the corrupted frame issue is solved, I recommend recalibrating with all the cameras stable and walking slowly through the whole overlapping area: ZED360 | StereoLabs
If a single PC cannot handle the full setup, the Fusion API also supports a Network Workflow, where each camera is handled by its own host machine streaming to a central fusion PC; this removes both the USB and the CPU bottlenecks.
Can you share a screenshot of your USB tree (Device Manager > Devices by connection, or USB Device Tree Viewer) with all four cameras connected? This will tell us exactly how the bandwidth is being shared.
